It is well known in the art to use glass fibers as reinforcements in the manufacture of polymeric composites. Typically, such fibers are manufactured by supplying glass in molten form to a bushing, drawing fibers from the bushing, and then gathering the fibers into a tow or strand. Usually, a sizing composition or chemical treatment is applied to the fibers after they are drawn from the bushing to protect the fibers from breakage during subsequent processing, and to improve the compatibility of the fibers with the matrix resins that are to be reinforced. Typically, the sizing compositions comprise one or more film-forming polymeric or resinous components, lubricants and glass-resin coupling agents dissolved or dispersed in water.
Polyester emulsions are well known and widely used as film formers in sizing compositions applied to glass fibers used in the reinforcement of polyester and vinylester materials, and are often used in the manufacture of continuous glass fiber reinforcement for filament winding and pultrusion operations. Typically the polyesters used in such sizing formulations are solids at room temperature, and are emulsified by first being dissolved in a suitable organic solvent such as styrene. However, the use of such solvent-containing emulsions in the sizing composition requires removal of the solvent after application of the sizing to the fibers, and increases the potential for release of volatile organic compounds (VOC's) into the work environment and atmosphere. In view of recent concerns over the effects of such VOC emissions, a need exists for a method for emulsifying such polyesters in water without the use of hydrocarbon solvents. Moreover, since the specific components of a particular sizing composition are usually carefully selected to provide optimum performance of the fibers in the intended reinforcement application, a need exists for a solvent-free method of emulsifying the polyesters used in present sizing compositions without deleteriously altering the chemical structure of the polyester. These needs are met by the process of the present invention described below.